Exploiting oleic acid to prepare two-dimensional assembly of Si@graphitic carbon yolk-shell nanoparticles for lithium-ion battery anodes

Carbon coating has been a routine strategy for improving the performance of Si-based anode materials for lithium-ion batteries. The ability to tailor the thickness, homogeneity and graphitization degree of carbon-coating layers is essential for addressing issues that hamper the real applications of Si anodes. Herein, we report the construction of two-dimensional (2D) assemblies of interconnected Si@graphitic carbon yolk-shell nanoparticles (2D-Si@gC) from commercial Si powders by exploiting oleic acid (OA). The OA molecules act as both the surface-coating ligands for facilitating 2D nanoparticle assembly and the precursor for forming uniform and conformal graphitic shells as thin as 4 nm. The as-prepared 2D-Si@gC with rationally designed void space exhibits excellent rate capability and cycling stability when used as anode materials for lithium-ion batteries, delivering a capacity of 1, 150 mAh·g^-1 at an ultrahigh current density of 10 A·g^-1 and maintaining a stabilized capacity of 1, 275 mAh·g^-1 after 200 cycles at 4 A·g^-1. The formation of yolk-shell nanoparticles confines the deposition of solid electrolyte interphase (SEI) onto the outer carbon shell, while simultaneously providing sufficient space for volumetric expansion of Si nanoparticles. These attributes effectively mitigate the thickness variations of the entire electrode during repeated lithiation and delithiation, which combined with the unique 2D architecture and interconnected graphitic carbon shells of 2D-Si@gC contributes to its superior rate capability and cycling performance.